Over the past five years, the importance of quinones in regulating biological systems has become increasingly evident. One of the major functions of this multifunctional class of molecules is the mediation of electron transport reactions. In these reactions quinones are one - or two - electron reduced to semiquinones or hydroquinones respectively. Being paramagnetic, the semiquinone has been detected with esr spectroscopy in several biological systems and has been shown to exhibit the powder spectrum associated with an immobilized radical. In order to better interpret the significance of these spectra, research must be conducted to investigate the environmental effects on the esr spectra of semiquinones in rigid media. Although the initial focus of this research proposal is on the environmental effects on the esr spectra of semiquinones in rigid media, the general theme is on the interactions experienced by all radicals in rigid media. The major sections of this research are as follows: (1) investigation of solvent-radical interactions; (2) investigation of the influence of ion-radical interactions at low temperatures; (3) study the esr spectra of semiquinone anions and neutral semiquinone at low temperatures; (4) detailed study of hydrogen bonding of radicals at low temperatures; (5) analysis of the anomalous saturation behavior of semiquinones at low temperatures. A Q-band microwave unit will be obtained to be used with the X-band esr spectrometer presently in our laboratory to aid in the complete study of radicals in rigid media. The research outlined above will greatly help us to understand the environment of radicals in biological systems.